Displacement detector systems are commonly used in many intrusion systems, and in security systems more generally. Most often, these detector systems are used to detect whether doors or windows are ajar or secured. A typical application for these detector systems is a door system that includes a door frame and a door. More generally, however, these detector systems can be used in other applications that require proximity and/or end position sensing, distance measurements such as nano-distance measurements, or moving part position sensing.
In these intrusion/security systems, the displacement sensor systems are typically monitored by a system control panel via a network. In this way, the control panel can monitor whether doors or windows are ajar or secured, for example.
Displacement detector systems are often constructed as two major pieces that work together as a pair. The two pieces are separated by a distance when installed. In these two-piece detector systems, one piece is mounted to a fixed surface, such as a door frame, and the other is attached to a traveling/moving object, such as a door. In a reed switch displacement detector system, for example, a reed switch as one piece is typically mounted to a door frame, and a magnet as the other piece is mounted to a door. When the magnet is brought into proximity of the reed switch, such as when the door is closed, the reed switch becomes conductive. A control panel connected to the reed switch can then monitor for changes in the conductivity of the reed switch to determine whether the door has opened. Other examples of two-piece detector systems include: a capacitive detector system having a capacitive sensor and a capacitance influence element as the two pieces; an inductive detector system having an induction sensor and an induction influence element as the two pieces; and an optical detector system having a light source and light sensor integrated within one piece, and a light reflector as the other piece.
Some displacement detector systems are also implemented as one-piece detector systems. Examples of these one-piece systems include one-piece accelerometer detector systems and one-piece optical detector systems.
An example of how a one-piece accelerometer detector system is installed at and operates within a door system is as follows. The detector system is usually installed by including the detector within a mortise of the door, but could also be mounted upon a surface of the door. When mounting the detector system upon the door, holes are drilled on the door's surface, and holes in a base of the detector system are aligned with the holes drilled in the door. Screws then fasten the base of the detector system to the door. When acceleration of the door exceeds a threshold, an accelerometer of the detector system is activated, thus detecting displacement of the door.
A one-piece optical detector system is typically installed at a door system as follows. The detector system is usually installed by mounting the detector system to the door frame, but could also be mounted to a surface of the door. The mounting of the optical detector system to the door frame or door is typically carried out in a similar fashion as the surface mounting of the accelerometer detector system described herein above.
Once mounted, the one-piece optical detector system generally operates as follows. The optical detector system has an integrated light source and light sensor. The light source emits a beam of light along a fixed optical axis to an object, such as to the door. The beam of light impinges upon a surface of the door, and the light sensor measures light reflected back from the door to determine a distance to the door. For the detector system to operate properly, the beam of light must impinge upon the door over a required travel range of the door. The optical detector system typically measures a distance to a closed door as a reference measurement, and compares new distance measurements obtained over time to the reference measurement to detect displacement of the door (i.e. to determine whether the door has opened).